The present invention relates to the acquisition and storage of data relating to a time dependent variable the value of which can vary over a wide range.
For many purposes, it is necessary to store data representing the values of a variable which can take on a wide range of values. Frequently, if the data is being generated over a period of time, a large number of storage locations must be made available for the storage of values.
By way of example, in a nuclear reactor flux monitoring system, flux detecting transducers generate pulses at a rate which is proportional to the reactor flux. The reactor flux can vary over a range of the order of eight decades, from 0.01 count per second to 1.times.10.sup.6 counts per second as the reactor goes from shutdown to full power output. The transducer output pulses will occur in a random pattern.
According to one known procedure, the pulses are counted during a succession of fixed time intervals each having a duration of the order of 100-125 milliseconds and the number of pulses produced during each time interval is stored in a respective memory location for subsequent processing.
At high pulse rates, a sufficient number of pulses is generated during each measuring interval to allow an accurate calculation of pulse rate after just a few intervals have elapsed.
However, when the pulse rate has a low value, monitoring must continue over a large number of intervals before an accurate pulse rate indication can be produced. For example, if the pulse rate has a nominal value of 0.1 pulse per second, only one pulse will occur, on average, during 100 intervals. Moreover, because of the random nature of the pulses, an accurate indication cannot be produced on the basis of a single pulse.
The accuracy with which an average pulse rate can be computed when the occurrence of pulses varies according to a Poisson distribution, can be estimated according to the following relationship: EQU error=1/square root of number of pulses.
For example, if 150 pulses are counted, the error would be be of the order of 8.16%. To achieve this accuracy at a nominal pulse rate of 0.01 pulse per second with measuring intervals of 100 milliseconds, the measuring operation would have to cover 150,000 intervals. If the data is stored in the form of representations of the number of pulses occurring during each interval, 150,000 memory locations would be required to store the data for performing one calculation.